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Chapter 4
Global Climates and Biomes
Global Processes Determine Weather
and Climate
• Weather- the short term conditions of the
atmosphere in a local area. These include
temperature, humidity, clouds,
precipitation, wind speed and atmospheric
pressure.
• Climate- The average weather that occurs
in a given region over a long periodtypically several decades.
Earth's Atmosphere
• Troposphere- the layer closest to Earth's
surface extending roughly 16 km (10 miles)
above Earth.
• Stratosphere- above the troposphere, this
extends from roughly 16 to 50 km (10-31
miles).
Unequal Heating of Earth
• As the Sun's energy passes through the
atmosphere and strikes land and water, it
warms the surface of Earth. But this
warming does not occur evenly across the
planet.
Unequal Heating of Earth
• This unequal heating is because:
• The variation in angle at which the
Sun's rays strike
• The amount of surface area over which
the Sun's rays are distributed
• Some areas of Earth reflect more solar
energy than others. (Albedo)
Atmospheric Convection Currents
• Air has four properties that determines its movement:
• Density- less dense air rises, denser air sinks.
• Water vapor capacity- warm air has a higher capacity
for water vapor than cold air.
• Adiabatic heating or cooling- as air rises in the
atmosphere its pressure decreases and the air expands.
Conversely, as air sinks, the pressure increases and the
air decreases in volume.
• Latent heat release- when water vapor in the
atmosphere condenses into liquid water and energy is
released.
Formation of Convection Currents
Formation of Convection Currents
• Atmospheric convection currents are global patterns of air
movement that are initiated by the unequal heating of
Earth.
• Hadley cells- the convection currents that cycle between
the equator and 30˚ north and south.
• Intertropical convergence- the area of Earth that receives
the most intense sunlight and where the ascending
branches of the two Hadley cells converge.
• Polar cells- the convection currents that are formed by air
that rises at 60˚ north and south and sinks at the poles (90˚
north and south)
Earth's Rotation and the Coriolis Effect
• As Earth rotates, its surface moves much
faster at the equator than in mid-latitude and
polar regions.
• The faster rotation speeds closer to the
equator cause a deflection of objects that are
moving directly north or south.
Earth's Rotation and the Coriolis Effect
• Coriolis Effect- the deflection of an object's
path due to Earth's rotation.
• The prevailing winds of the world are
produced by a combination of atmospheric
convection currents and the Coriolis effect.
Earth's Tilt and the Seasons
• The Earth's axis of rotation is tilted 23.5 ˚.
• When the Northern Hemisphere is tilted
toward the Sun, the Southern Hemisphere is
tilted away from the Sun, and vice versa.
Ocean Currents
• Ocean currents are driven by a combination of
temperature, gravity, prevailing winds, the
Coriolis effect, and the locations of continents.
• Warm water, like warm air, expands and rises.
• Gyres- the large-scale patterns of water
circulation. The ocean surface currents rotate in
a clockwise direction in the Northern
Hemisphere and a counterclockwise direction in
the Southern Hemisphere.
Upwelling
• Upwelling- as the surface currents separate
from one another, deeper waters rise and
replace the water that has moved away.
• This upward movement of water brings
nutrients from the ocean bottom that
supports the large populations of
producers, which in turn support large
populations of fish.
Thermohaline Circulation
• Thermohaline circulation- another oceanic
circulation that drives the mixing of surface
water and deep water.
• Scientists believe this process is crucial for
moving heat and nutrients around the
globe.
• Thermohaline circulation appears to be
driven by surface waters that contain
unusually large amounts of salt.
Thermohaline Circulation
Thermohaline Circulation
• Some of the water that flows from the Gulf of
Mexico to the North Atlantic freezes or
evaporates, and the salt that remains behind
increases the salt concentration of the water.
• This cold, salty water is relatively dense, so it
sinks to the bottom of the ocean, mixing with
deeper ocean waters.
• These two processes create the movement
necessary to drive a deep, cold current that
slowly moves past Antarctica and northward to
the northern Pacific Ocean.
Heat Transport
• Ocean currents can affect the temperature of
nearby landmasses.
• For example, England's average winter
temperature is approximately 20 ˚ C (36˚F)
warmer than Newfoundland, Canada,
which is located at a similar latitude.
El Nino-Southern Oscillation
• Every 3 to 7 years, the interaction of the
Earth's atmosphere and ocean cause surface
currents in the tropical Pacific Ocean to
reverse direction.
El Nino-Southern Oscillation
• First, the trade winds near South America weaken.
• This weakening allows warm equatorial water from the
western Pacific to move eastward toward the west coast of
South America.
• The movement of warm water and air toward South
America suppresses upwelling off the coast of Peru and
decreases productivity there, reducing fish populations
near the coast.
• These periodic changes in wind and ocean currents are
collectively called the EL Nino-Southern Oscillation, or
ENSO.
Rain Shadows
Rain Shadows
• When air moving inland from the ocean that contains a large
amount of water vapor meets the windward side of a mountain
range (the side facing the wind), it rises and begins to experience
adiabatic cooling.
• Because water vapor condenses as air cools, clouds form and
precipitation falls.
• The presence of the mountain range causes large amounts of
precipitin to fall on its windward side.
• The cold, dry air then travels to the other side of the mountain
range (the leeward side), where it descends and experiences higher
pressures, which cause adiabatic heating.
•
This air is now war and dry and process arid conditions on the
leeward side forming the region called a rain shadow.
Variations in Climate Determine the
Dominant Plant Growth Forms of
Terrestrial Biomes
• Climate affects the distribution of species
around the globe.
• Organisms possess distinct growth forms
due to adaptations to local temperature and
precipitin patterns.
• Biomes- The presence of similar plant
growth forms in areas possessing similar
temperature and precipitation patterns.
Tundra
• Cold, treeless biome with low-growing
vegetation. In winter, the soil is completely
frozen.
• The tundra's growing season is very short,
usually only about 4 months during
summer.
• The underlying subsoil, known as
permafrost is an impermeable, permanently
frozen layer that prevents water from
draining and roots from penetrating.
Tundra
Boreal Forest
• Forests made up primarily of coniferous (conebearing) evergreen trees that can tolerate cold
winters and short growing seasons.
• Boreal forests are found between about 50˚ and
60˚ N in Europe, Russia and North America.
• This subarctic biome has a very cold climate, and
plant growth is more constrained by temperature
than precipitation.
• The soil is nutrient-poor due to slow
decomposition.
Boreal Forest
Temperate Rainforest
• Moderate temperatures and high precipitation typify the temperate
rainforest.
• The temperate rainforest is a coast biome and can be found along the
west coast of North America from northern California to Alaska, in
southern Chile, on the west coast of New Zealand, and on the island
of Tasmania.
• The ocean currents help moderate temperature fluctuations and
provide a source of water vapor.
• This biome has a nearly 12-month growing season where winters are
rainy and summers are foggy.
• The mild temperatures and high precipitation supports the growth of
very large trees.
Temperate Rainforest
Temperate Seasonal Forest
• Receive over 1 m (39 inches) of precipitation
annually.
• Found in the eastern United States, Japan,
China, Europe, Chile and eastern Australia.
• Dominated by broadleaf deciduous trees
such as beech, male, oak and hickory.
• Warmer summer temperatures favor
decomposition so soils generally contain
more nutrients than those of boreal forests.
Temperate Seasonal Forest
Woodland/Shrubland
• Found on the coast of southern California,
southern Australia, southern Africa and in the
area surrounding the Mediterranean Sea.
• Hot, dry summers and mild, rainy winters are
characteristic of this biome.
• There is a 12-month growing season, but plant
growth is constrained by low precipitin in
summer and by relatively low temperatures in
winter.
• Wildfires are common and plants of this biome
are well adapted to both fire and drought.
Woodland/Shrubland
Temperate Grassland/Cold Desert
• This biome has the lowest average annual precipitation of
any temperate biome.
• These are found in the Great Plains of North America, in
South America, and in central Asia and eastern Europe.
• Cold, harsh winters and hot, dry, summers characterize
this biome.
• Plant growth is constrained by both insufficient
precipitation in summer and cold temperatures in winter.
• Plants include grasses and non woody flowering plants
that are well adapted to wildfires and frequent grazing by
animals.
Temperate Grassland/Cold Desert
Tropical Rainforest
• In the tropics, average annual temperatures exceed 20˚C.
• This biome is located approximately 20˚ N and S of the
equator.
• They are found in Central and South America, Africa,
Southeast Asia, and northeastern Australia.
• Precipitation occurs frequently and this biome is warm
and wet with little temperature variation.
• Tropical rain forests have more biodiversity per hectare
than any other terrestrial biome and contain up to twothirds of Earth's terrestrial species.
Tropical Rainforest
Tropical Seasonal Forest/Savanna
• Warm temperatures and distinct wet and dry seasons
characterize this biome.
• Tropical seasonal forests are common in much of Central
America, on the Atlantic coast of South America, in
southern Asia, in northwestern Australia, and in subSaharan Africa.
• Soil in this biome is fairly fertile and can be farmed due to
high decomposition rates, but the low amount of
precipitation constrains plants from using the soil
nutrients that are released.
• Grasses and scattered deciduous trees are common.
Tropical Seasonal Forest/Savanna
Subtropical Desert
• This biome is found at 30˚ N and S with hot
temperatures and extremely dry conditions.
• The Mojave Desert in the southwestern
United States, the Sahara in Africa, the
Arabian Desert of the Middle East and the
GReat Victoria Desert of Australia are all
subtropical deserts.
• Cacti, euphorbs and succulent plants are
well adapted to this biome.
Subtropical Desert
Aquatic Biomes are Categorized by
Salinity, Depth, and Water Flow
Streams and Rivers
• Flowing fresh water that may originate
from underground springs or as runoff
from rain or melting snow.
• Streams are typically narrow and carry
relatively small amounts of water where
rivers are usually wider and carry larger
amounts of water.
Lakes and Ponds
• Standing water that some of which is too
deep to support emergent vegetation.
• Lakes are larger than ponds but there is no
clear point at which a pond is considered
large enough to be called a lake.
Lakes and Ponds
Lakes and Ponds
• Littoral zone- the shallow area of soil and water near the
shore where algae and emergent plants grow.
• Limnetic zone- open water, where rooted plants can no
longer survive. Phytoplankton are the only
photosynthetic organisms. This zone extends to as deep
as sunlight can penetrate.
• Profundal zone- the zone where sunlight cannot
penetrate and therefore producers cannot survive.
• Benthic zone- the muddy bottom of a lake or bond
beneath the limnetic and profundal zone.
Freshwater Wetlands
• Aquatic biomes that are submerged or
saturated by water for at least part of each
year, but shallow enough to support
emergent vegetation.
• These include swamps, marshes, and bogs.
Salt Marshes
• Found along the coast in temperate climates
and contain non woody emergent
vegetation.
• The salt marsh is one of the most productive
biomes in the world.
Mangrove Swamps
• Found along tropical and subtropical coasts
and contain trees whose roots are
submerged in water.
• Mangrove trees are salt tolerant and help
protect the coastlines from erosion and
storm damage.
Figure 4.32
Intertidal Zone
• Narrow band of coastline that exists
between the levels of high tide an low tide.
• Waves that crash onto the shore in this
biome can make it a challenge for organisms
to hold on and not get washed away.
Figure 4.33
Coral Reefs
• Found in warm, shallow waters beyond the
shoreline.
• Earth's most diverse marine biome even
though coral reefs are found in water that is
relatively poor in nutrients and food.
• Coral bleaching- when the algae inside the
coral dies. Scientists believe this is due to a
combination of disease and environmental
change.
The Open Ocean
• The depth that light can penetrate in the open
ocean is dependent on the amount of sediment
and algae suspended in the water.
• Photic zone- the zone that receives enough light
to allow photosynthesis to occur.
• Aphotic zone- the deeper water that lacks
sufficient light for photosynthesis.
• Chemosynthesis- The process that occurs in the
aphotic zone when some species of bacteria use
methane and hydrogen sulfide to generate
energy.